Spark plug



OC- 8, 1929. H. RABEZZANA ET Al. 1,731,203

SPARK PLUG Filed Nov. l5. 1925 2 Sheets-Sheet l mil-1MM Oct. 8, 1929.

H. RABEZZANA Er AL 1,731,203

SPARK PLUG Filed Nov. 13, 1925 2 Sheets-Sheet 2 55% f, @IMM 611%' Patented ocr. 8,1929

UNITED STATES PATENT OFFICE HECTOR RABEZZANA AND DONALD 'i RANDOLPH, 0F FLIN'I, MICHIGAN', ASSIGNOBS TO A. C SPARK PLUG COMPANY, F FLINT, MICHIGAN, A COMPANY OF MICHIGAN SPARK PLUG Application inea november 13, 1925. serial No. 68,809.

One of the chief problems involved in the design of spark plugs for use in high compression engines such as are employed in racing machines and aeroplanes is that of disposing of the heat which is absorbed by the lower portions of the central electrode and the surrounding insulator. If this heat is not rapidly carried away such high temperatures will soon be built up in the insulator that its electrical resistance will be reduced and it may even become red hot and cause pre-ignition of the explosive mixture. As the portion of the insulator adjacent the central electrode is the hottest part of it, it is particularly essential that this electrode be well cooled.

In this application we have disclosed a new design of plug which has for its purpose the overcoming of the diliiculties above described. To facilitate the transfer of heat away from the lower portion of the central electrode, thereby reducingthe amount of heat passing from the electrode to the insulator, we have made this electrode very short so that the path of travel of heat to the cooled upper portion of the electrode is reduced to a minimum.

7e have also preferably provided the electrode with cooling means which may consist' of spaced lins extending outwardly from the plug and subject to the cooling elcct of air conduction or air draft.

As another means of assisting in the cooling of the plug we have thickened the portions of the shell which form the path for the conduction of heat from the insulator to the cooler portions `of the motor. By thus broadening the path fpr the conduction ofheat, the rate of flow is increased.

With the construction so far described we have preferably combined the feature of employing an insulator having a ground, conical-shaped lower portion adapted to closely fit in a conical seat in the shell, as described and claimed in my prior application Serial.

No. 749,414 tiled Nov. 12, 1924. We have thus secured much better contact between the insulator and the vshell thereby reducing the resistanceto the flow of heat.

. Referring to the drawings: v

Figure 1 is a longitudinal sectional view of one form of my improved spark plug;

Figure 2 is a section on line 2 2 of Figure 1;

Figure 3 is a view showing a slight modification of the construction of Figure 1;

Figure 4 is a longitudinal'sectional -view of a'modified form; l

Fi gurel 5 is a top plan View of Figure 3; and

Figure 6 is a section on line 5-5 of Figure 3..

The preferred form of our improved spark plug is shown in Figures 1 and 2. In these figures the reference character 2 indicates the insulator which is mountedwithin the shell 4. Passing centrally through the insulator is the electrode 6 while the cooperating electrode is mounted on the shell in any preferred manner.

A distinguishing feature of this plug is the shortness 4of the central electrode and insulator for purposes of cooling. To increase the rate of cooling the upper end of the electrode is provided with 'special cooling means which may consist of fins or disks 10 exposed to the air currents. While the fins may be secured on the electrode by any preferred method or may be formed integrally with the electrode, we have illustrated a constructionvin which the disks are slipped over the .upper end of the electrode with spacing collars between them and are secured in position by a .clamping nut 14. Preferably the disks and collars are provided with radial grooves 15 and 15 and in the assembly of the plug rings of solder, preferably of silver' composition, are slipped over the collars 12, the whole being then subjected to a heating operation which results in a flow of the solder along the radial passages 15 and 15', thus secured t-hc disks to the electrodes 6 in good heat conducting relation. Of course, if preferred, the ins may be secured in place by brazing or welding.

The electrode is also preferably formed of two metals, the lower portion 16 which is made of nickel or some other material which is not subject to corrosion being welded. or otherwise secured to the upper portion 18 which may be of copper or some other metal which' isa good conductor of heat. If preferred, the electrode may be made entirely of some good heatconducting material Asuch as and the central electrode is formed with an upwardly extending annular rib 20`to `increase the length of the path of travel for leakage currents which follow the surface of the insulator. This rib defines a depression 2l in the upper portion of the insulator permitting the cooling air currents to strike the electrode further down in its length thus permitting a further effective reduction in the length of the saidelectrode. It will be noted that the fins or disks Al are upwardly flared to conform to the flaring of the inner surface of the rib 20. A To increase the rate of cooling we havev employed, in addition, the feature of forming a very close fit between the lower portion of the insulator and the shell so that heat will be rapidly conducted away from the former. Thus the lower portion of the shell is provided with a conical seat 22 receiving the conical portion 24 of the insulator without the in erposition of the usual gasket.

y This provides an extended contact area and eliminates one of the joints across which the heat must travel in the ordinary plug.

It will also be noted that we have thick.- ened the lower portion 26 of the shell which contacts with the cylinder head or other part in which the plug is mounted. This has the effect of broadening. the path traversed by the heat as well as affording a greater mass of material for the absorption thereof with the result that coolingis facilitated. This cooling action is rendered effective by the fact that the central electrode projects into a space inside the shell in which there is very ylittle circulatioirof gases ,so that heat withdrawn from said space is but slowly replaced. Con-l sequently, by providing forthe removal of heat at an increased rate equilibrium of heat flow is established at a lower temperature than with previous constructions. VVhile in this form we have provided for the increased rate of removal of heat merely by' thickening the walls of the surrounding shell, wemay also resort to grooving or serrating the said walls as illustrated in connection with the` construction shown in Figures 4,'to 6, this feature forming the subject matter of my pri or application Serial No. 44,867, filed July e0, 1925. i

With a plug made as above described it will be apparent that cooling of the hottest portion thereof, 'that is, the lower part of the central electrode and the lower part of the insulator is facilitated by shortening the insulator and the said electrode, by providing G the latter with cooling tins, by providing better contact between the insulator and they shell and by thickening the lower portion of the latter. We have found by actual experiment that a plug made in this manner may be maintained at a lower temperature when subjected to\ eXtreme heat than any plugs heretofore designed.

While we'have attempted to explain the causes which have produced this result it is not possible to ascertain with accuracy the eXact heat relations which obtain in the plug and we accordingly do not wish to be limited by the statement of theory herein set forth. The construction shown in Figures l and2 may be modified as shown in Figure 3 by the interposition of the gasket between the Iporcelain and the shell. The use of a gasket such as shown avoids the necessity for such eXactness in the` grinding of the contacting portions 22` and 24 of the shell and insulator. While the gasket 50 might be in the form of a frusto-conical band of uniform thickness we have preferred to illustrate a gasket having portions of reduced thickness between its ends, said portions contacting only with the inner wall of the shell. We are thus enabled to increase the pressure per unit area between the contacting surfaces of the gasket and in-v sulator, a feature disclosed and claimed in the application ofAlbert Champion, `Serial No. 19,345, filed March 30, 1925. If desired, the intermediate portion 52 of the gasket 50 may be omitted. Y

In the modified form shown in Figures 4 to 6,' 30 indicates the insulator, 32fthe shell, 34 the central electrode36 the side electrode. In this form of the invention gaskets 38 are provided between the insulator andthe lower portion of the shell. The interior of this portion of the shell is also preferablyprovided with ribs 40 as previously described. In this embodiment the' cooling fins 42 are integral with the electrode. A

In this type of plug the central electrode is better insulated to prevent the plug from becoming too easily fouled.

- We claim:

y1. A spark plug comprising a shell, an insulator in the shell, an electrode passing .through the insulator, said electrode being modied from standard practice in that it is relatively short to permit rapid conduction of heat therefrom, the lower portion of said shell being ingood conducting relation withv the insulator, and with the engine, said lower portion being of increased thickness forthe ready transfer of heat, said electrode being provided with heat-radiating fins atits upper portion.

2. A spark plug Ycomprising a shell having a conical seat, an insulator having a conical lower portion for engagement with said seat, an electrode passing through the insulator, said electrode being modified from standard practice in that it is relatively short to afford a good path for the conduction of heat therefrom, the lower portion of said shell which is -in good conducting relation with the insulator and with the engine being of increased thickness to facilitate the transfer of heat.

3. A spark plug comprising a shell having a conical seat between its ends,an insulator having a conical lower portion in direct engagement with said seat, an electrode passing through said insulator, the ends of said electrode and insulator stopping short of the lower'end of the shell, an electrode carried by the shell and extending inwardly from the lower' end thereof, said first-named electrode being modified from standard practise in that it is relatively short' to afford a good path for the conduction of heat from the lower end thereof, and cooling ribs carried by the upper end of'said electrode.

4. A spark plug comprising a shell having a conical seat between its ends, said shell being provided with a thickened lower end having external` threads thereon, an insulator having a conical lower portion in direct engagement with said conical seat, an electrode passing through said insulator, the ends of said electrode and insulator' stopping short of the lower end of the shell, an electrode carried by the shell and extending inwardly from 3o the lower end thereof, said first-named electrode being modified from standard practise in that it is relatively short to afford a good path for theconduction of heat from the low'- er end thereof, said insulator being provided at its upper end with a rib to increase the surface insulation.

5. A spark plug comprising a shell, an insulator 'in the shell, an electrode passing centrally through the insulator and being provided at its upper end with a cooling fin wholly clearing` the insulator and directly exposed to the cooling action of passing air currents, said electrode being made of good heat conducting` material solid in cross-secshell, said upper end of the insulator being provided with a protuberant rio to increase the surface insulation, an electrode passing centrally through the insulator and being provided at its upper end with a cooling fin wholly clearing the insulator and directly exposed to the cooling action of passing air currents, said electrode being made of good heat conducting material solid in cross-section to tion to permit maximum heat transfer, and

permit maximum heat transfer, and being modified from standard practice in that it is relatively short so that the difference in temperature between the electrode at the cooling fin and the surrounding atmosphere is sufliciently great to permit effective cooling.

7. A spark plug comprising a shell provided with the usual side electrode, a central electrode, and an insulator in the shell, the upper end of the insulator being. provided with an annular depression lsurrounding the center wire and providing a rib on the insulator to increase the surface insulation, said central electrode being provided at its upper end with a cooling fin wholly clearing the insulator and directly exposed to the cooling action of passing air currents, said electrode being made of good heat conducting material solid in cross-section to permit maximum heat transfer, l and said central electrode being modified from standard practice in that it is relatively short so that the difference in temperature between the electrode at the cooling fin and the surrounding atmosphere is sufficiently great'to permit effective cooling.

8. A spark plug comprising a shell having a conical seat between its ends, a central electrode. and an insulator in the shell having a conical lower portion in direct engagement with said seat, the upper end of the insulator being provided with a protuberant rib to mcrease the surface insulation, said central electrode being provided at its upper end with a cooling fin wholly clearing the insulator and directly exposed to the cooling action of passing air currents, said electrode being made of good heat conducting material solid 1n cross-section to permit maximum heat transfer, and said electrode being modified from standard practice in that it is relatively short so that the difference in temperature between the electrode at the cooling fin and the surrounding atmosphere is sufficiently great to permit effective cooling.

In testimony whereof we afiix our signatures.

l HECTOR RABEZZANA.

DONALD. W. RANDOLPH. 

